1. Field of the Invention
The present invention relates to a positive electrode of a lithium ion secondary battery, and a method of manufacturing a lithium ion secondary battery.
2. Description of Related Art
A lithium ion secondary battery is chargeable or dischargeable by lithium ions in an electrolyte moving between a positive electrode and a negative electrode which store and release lithium ions.
Published Japanese Translation of PCT application No. 2002-527873 (JP-A-2002-527873) discloses a technique regarding a lithium ion polymer battery. In the technique disclosed in JP-A-2002-527873, in order to improve battery characteristics, an insoluble lithium compound such as Li3PO4 or LiF is added to the lithium ion polymer battery. In addition, as a cathode material, a manganese oxide compound (LiMn2O4, LiMnO2) is used.
One of the important characteristics of a lithium ion secondary battery is the cycle characteristics. The cycle characteristics are an index indicating to what extent a battery capacity of a lithium ion secondary battery after repetition of charging and discharging in predetermined cycles changes as compared to an initial battery capacity. In general, it is preferable that a decrease in the battery capacity after the repetition of charging and discharging be small as compared to the initial battery capacity.
In the technique disclosed in JP-A-2002-527873, in order to improve battery characteristics, an insoluble lithium compound such as Li3PO4 or LiF is added to the lithium ion polymer battery. However, as a result of investigation, the present inventors initially found that, in a lithium ion secondary battery in which lithium nickel manganese oxide is used as a positive electrode active material, cycle characteristics of the lithium ion secondary battery cannot be improved to a sufficient value with only the addition of Li3PO4 or LiF.